Method of removing sulfur oxides and nitrogen oxides by dry process

Abstract

This invention relates to a method of removing sulfur and nitrogen oxides by a dry process comprising passing a waste gas through a bed of a carbonaceous adsorbent to remove sulfur oxides and adding ammonia to remove nitrogen oxides, characterized in that at least two carbonaceous adsorbent beds are used and the carbonaceous adsorbent used mainly for removal of sulfur oxides is further used for treatment of the waste gas leaving the final carbonaceous adsorbent bed to remove the ammonia.

What is claimed is: 
     
       1. A method of removing sulfur and nitrogen oxides from waste gases which comprises passing transversely a waste gas through a first carbonaceous adsorbent bed moving vertically, in which the most part of SOx is removed, adding ammonia in an excessive amount to the waste gas leaving the first bed, passing the waste gas through a second carbonaceous adsorbent bed moving vertically in parallel to the first bed as to the flow of carbonaceous adsorbent, in which the residual SOx is removed and NOx is decomposed and removed, then passing the waste gas leaving the second bed and containing unreacted ammonia through a third bed of a part or all of the carbonaceous adsorbent moving vertically from the first bed, in which the unreacted ammonia is removed, and regenerating and reusing the carbonaceous adsorbent from the first bed. 
     
     
       2. The method of removing sulfur and nitrogen oxides as claimed in claim 1, wherein the ammonia is added in the form of ammonia gas alone or diluted with another gas. 
     
     
       3. The method of removing sulfur and nitrogen oxides as claimed in claim 1, wherein the carbonaceous adsorbent is at least one member selected from the group consisting of activated carbons, activated cokes and semi-cokes. 
     
     
       4. The method of removing sulfur and nitrogen oxides as claimed in claim 1, wherein the removing of sulfur and nitrogen oxides is carried out at a temperature of 110° to 170° C. 
     
     
       5. The method of removing sulfur and nitrogen oxides as claimed in claim 1, wherein the removing of sulfur and nitrogen oxides is carried out at a space velocity of at most 3,000 hr -1 . 
     
     
       6. The method of removing sulfur and nitrogen oxides as claimed in claim 1, wherein the removing of ammonia is carried out at a space velocity of at most 20,000 hr -1 . 
     
     
       7. A method of removing sulfur and nitrogen oxides from waste gases which comprises providing a first bed, second bed, third bed and fourth bed each of which consists of a carbonaceous adsorbent moving vertically, the first bed and the fourth bed, and the second bed and the third bed being arranged in series as to the flow of carbonaceous adsorbent, passing a part of the carbonaceous adsorbent through the first bed to the fourth bed and the residual and most part of the carbonaceous adsorbent through the third bed to the second bed, passing transversely a waste gas through the first by adsorption of the SO x  onto the carbonaceous adsorbent in the form of sulfuric acid adding ammonia to the waste gas from the first bed, passing the waste gas through the second bed in which the most part of SOx is removed and a part of NOx is decomposed and removed, adding further ammonia in an excessive amount to the waste gas from the second bed, passing the waste gas through the third bed in which the residual parts of SOx and NOx are removed, then passing the waste gas from the third bed through the fourth bed in which the unreacted ammonia is removed by a carbonaceous adsorbent carrying sulfuric acid, and regenerating and reusing the carbonaceous adsorbent discharged from the second bed and the fourth bed. 
     
     
       8. A method of removing sulfur and nitrogen oxides from waste gases which comprises providing a first bed, second bed and third bed each of which consists of a carbonaceous adsorbent moving vertically in this order said beds being arranged such that the second bed in on top, and the first and third beds being located underneath, and in series as to the flow of carbonaceous adsorbent, passing the carbonaceous adsorbent through the second bed to the first bed, a part of the adsorbent leaving the first bed being passed through the third bed and subjected to regeneration, passing a waste gas through the first bed in which the most part of SOx is removed by adsorption of the SO x  onto the carbonaceous adsorbent in the form of sulfuric acid adding ammonia in an excessive amount to the waste gas from the first bed, passing the waste gas through the second bed in which the residual part of SOx is removed and NOx is decomposed and removed, and then passing the waste gas containing the unreacted ammonia, through the third bed in which the unreacted ammonia is removed by the sulfuric acid containing adsorbent. 
     
     
       9. A method of removing sulfur and nitrogen oxides as claimed in claim 8 in which ammonia is also added to the waste gas which passes through the first bed in which most of the SO x  is removed.